Kate Middleton and Prince William are marking Prince Louis’ 6th birthday with a “private party,” The Post can reveal.

As the youngest son of the Prince and Princess of Wales rings in his birthday Tuesday, the royals are making sure that his special day will be “as normal and as much fun” as possible considering the difficult few months the family has been faced with.

“With Kate’s health — and knowing what Kate is like as a person — she wants her son to have the best birthday possible, like any mother,” a palace insider told The Post.

“She’s still going to try to make sure the day is as normal and as much fun for that child as possible, especially when they’re of that young age.”

Middleton, 42, is currently in the thick of her cancer treatment following her diagnosis earlier this year. In March, she revealed that she’s undergoing chemotherapy.

Still, she’s made sure that Louis’ birthday party is just as fun as in years past, according to King Charles’s former butler.

“In the past, there have been birthday parties where friends have been invited, with little George there were friends invited for parties and I believe Kate would have organized that,” Grant Harrold exclusively told The Post.

“Celebrations will be more reserved and low key and there might not be a party with other children like there has been in previous years,” he added.

The couple marked their son’s birthday Tuesday by posting a sweet snap of him smiling while lying down on a picnic blanket in the grass.

“Happy 6th Birthday, Prince Louis! 🎂 Thank you for all the kind wishes today,” they captioned the snap shared on X and Instagram.

In 2019, Middleton revealed that she likes to bake her own cakes for her children on their birthdays, and typically stays up until 12 to do so.

It’s unclear if her current health has allowed her to continue the tradition this year.

“Kate’s health will be a priority, but she’ll still want Louis to have as much fun as possible — how that takes shape, they may want to choose to keep private,” Harrold said.

“As a family, however, you can guarantee they will still be celebrating his birthday in some form and as normal as possible to make it a memorable day.”

“They’re a very private family as we know and I can imagine on this occasion, I’m sure it’ll be a private family occasion,” he added.

And, Prince Louis isn’t the only one in the royal family with a spring birthday – on May 2, Princess Charlotte will turn 9.